1. Field of the Invention
This invention relates to a fixing apparatus which fixes a developer image on paper and an image forming apparatus provided with the fixing apparatus, such as a copying machine or a printer.
2. Description of the Related Art
In the field of fixing apparatus installed in copying machines using electrophotographic processes, a fixing apparatus which includes an induction heating unit that generates hear by use of an electromagnetic induction has recently been put to practical use. In many cases, a heating (fixing) roller in which a heater is set and a pressure roller pressed against the heating roller at a specific pressure at one point of the outer circumference of the heating roller are used. It is well known that such a configuration enables not only the heat of the heating roller to be supplied to toner efficiently but also pressure for fixing the melted toner to a transfer medium to be applied to the transfer medium and toner efficiently.
One known fixing apparatus using induction heating is such that, for example, the magnetic flux leaking from the induction coil provided outside the fixing roller is suppressed by a shield member, which enhances the heat dissipation of the induction coil (Jpn. Pat. Appln. KOKAI Publication No. 2001-313162).
Another known induction heating fixing apparatus with exciting coil outside the rotating body is such that the arrangement of a magnetic material on the opposite side of the rotating body of the exciting coil not only increases the heat generation efficiency but also prevents the magnetic field produced from the exciting coil from leaking to the adjoining parts (Jpn. Pat. Appln. KOKAI Publication No. 11-297462).
A further known induction heating fixing apparatus is such that an induction heating member, a film member for moving the heating member, and an exciting coil fixing member have a ferromagnetic, high-sensitivity shield member, thereby preventing electromagnetic noise leaks (Jpn. Pat. Appln. KOKAI Publication No. 9-16006).
In an image forming apparatus with a heating unit using such induction heating, the high-frequency magnetic field generated from the coil can reach the circuit board in the apparatus or the printer controller or FAX controller optionally installed, which results in the problem of causing the devices or units to malfunction.
In addition, when a thin-film conductive member is used for induction heating to increase the efficiency in producing rapid temperature changes, or when the temperature is raised from room temperature to the requested fixing temperature (in warm-up), the high-frequency magnetic field generated from the coil can have a greater effect on the units in the apparatus.
Furthermore, even when a shield member is used, the high-frequency magnetic field from the coil can leak from the spacing or the like to secure a space through which the transfer medium is to be transported.